1. Field of the Invention
The present invention relates to a woven or non-woven glass mat; and more particularly, to a woven or non-woven glass mat suited for use as an attached or embedded backing of a vinyl floor covering to accommodate floor dimensional changes due to temperature variations and floor bending stresses resulting in expansion or contraction of floor surface.
2. Description of the Prior Art
Vinyl floor coverings are commonly used in the construction industry in a wide variety of applications including domestic and industrial floorings. Vinyl floor coverings provide easy installation, availability of varied geometric textures, colors, and patterns. When the vinyl floor covering is unreinforced, it has a tendency to sag, and change shape in rolls that are sold, depending on how they are rolled and stored. Furthermore, the vinyl floor covering may acquire permanent creases, and may not lie flat on the floor during installation. Non-glass reinforced material may also expand, contract, curl, blister, or tear with changes in temperature and relative humidity.
The vinyl sheet floor covering utilizes a backing or reinforcing material that is part of the construction. The backing surface directly contacts the floor surface upon installation of the floor covering. Glass fiber mats are considered very desirable backings for floor coverings, despite certain limitations inherent to such backings. Specifically, when the sub floor is composed of wood or other materials, the floor tends to expand and contract beyond the ability of the glass mat backing. For this reason, manufacturers use a felt or paper back in North America where most floors are wooden and the flooring is glued in place. In Europe most floors are composed of concrete, and experience very little expansion and contraction. As a result, most European vinyl floor coverings have a glass mat backing that takes advantage of the dimensional stability of glass and does not require gluing.
The relative dimensional stability of such glass fiber reinforced vinyl floor coverings is desirable when installed over concrete, but may cause problems when installed over a wood sub-floor. Wood sub-floors exhibit relatively large dimensional changes in response to temperature and humidity changes. In wintertime, wood sub-floors tend to dry out, shrinking the wood by as much as 0.5%. Unless the floor covering is able to compress (i.e., shrink) along with this dimensional change in the sub-floor, the floor covering may respond by buckling.
Vinyl floor coverings have been reinforced with glass fiber backing in order to provide some structural rigidity. The glass fibers, in the form of woven or non-woven glass fibers, is bonded to the underside of the vinyl floor covering; on the surface opposed to the texture, color, and pattern of the show surface. When the vinyl floor covering is installed on a wooden, or other sub-flooring, the vinyl floor covering may separate from the sub-flooring when the floor is under stress or expands/contracts due to thermal excursions. The vinyl floor covering having a glass fiber mat on its underside does not elongate or compress to maintain the shape of the sub-flooring. As a result the bond between the vinyl floor covering provided with the glass fiber underside reinforcement and the sub-flooring is broken at highly stressed locations. This results in eventual separation of the vinyl floor covering from the sub-flooring, creating unsightly ‘bubbles’ or lifted edges, and ultimately requiring a complete replacement of the vinyl floor covering. In cases where the bond to floor remains, the glass mat may tear, creating pattern distortions and ripples.
A number of patents discuss various fiber reinforcement strategies for vinyl floor coverings.
U.S. Pat. No. 2,800,423 to De Swart (hereinafter the '423 patent) discloses a molded article of stretchable glass fiber cloth, which is readily stretchable in all directions in the plane of the fabric. The glass fiber cloth itself is generally not stretchable and is a complex polymeric cloth with glass fiber reinforcement that requires cutting the glass cloth into small shaped pieces. According to the '423 patent disclosure, the non-elastic fiber fabric is provided with a number of slits that allows the stretching of the glass fabric. Specifically, the '423 patent discloses a molded article of stretchable glass fiber cloth. The stretching of the glass fiber occurs prior to the molding operation wherein the glass fiber is free to stretch. Once the glass fiber cloth is molded within the polymeric matrix, the glass fiber is not stretchable. There is no hint or suggestion that the polymeric matrix having the slitted glass fiber cloth has the ability to accommodate expansion and contraction tensions. This is not a vinyl floor covering, but is rather a molded polymer which has glass fiber cloth with slits provided as a reinforcement.
U.S. Pat. No. 5,080,944 and its divisional U.S. Pat. No. 5,188,874 to Kauffman et al. (hereinafter the '944 patent) discloses a hybrid floor covering. The object of the invention is to provide a vinyl floor covering that accommodates wood sub-floor contraction and expansion as well as rolling load. The floor covering incorporates a foamed plastisol encapsulated glass mat, which may be cut to form pivot points and expanded under a controlled pre-stressed condition. The glass mat serves as a carrier during manufacture, and acts as an “elastic glass” reinforcing layer during use for either tension or loose-lay flooring. The floor covering may be a true hybrid surface covering capable of accommodating the dimensional change of a target sub-floor by utilizing the characteristics of both tension floorings and loose-lay floorings. The resilient floor covering disclosed in the '944 patent has a matrix surrounding a reinforcing layer. The matrix with the surrounding reinforcing layer is modified by chemical or mechanical means to have relaxed compressive and tensile stiffness so that it will elongate under tension and resist bending under compression. The floor covering may be used as a loose lay surface covering or as a tension surface covering over wooden sub-floors comprising a reinforcing layer having regions of differential relaxed compressive/tensile stiffness. The reinforcing layer is formed by a pattern of line segments comprising a plurality of substantially parallel and linearly spaced first line segments and second line segments which are non-intersecting. The segments form pivot points cooperating such that the surface covering product is elongated in a direction generally transverse to an applied tensile stretching force. The surface covering having a reinforcing layer that is an expandable diagonal patterned glass mat as illustrated in FIG. 1 and FIG. 2 of the '944 patent in which the glass mat is encapsulated with a plastisol. Because of the controlled pre-stressed condition of the reinforcing layer, the adjacent sides of the slits are pulled apart. The slits interact to form pivot points, which cooperate such that the reinforcing layer is capable of increasing in dimension and decreasing in dimension, respectively, in a direction generally transverse to an applied tensile or compression force. The fiber mat is cut along mutually non-intersecting line patterns so as to form pivot points that enlarge the cut lines, creating expansion of the mat. Since glass fibers do not elongate in length, expansion can be only be accommodated by slippage of the glass fibers within the plastisol encapsulation. There is no possibility of increasing the length of the floor covering unless the fibers slip within the plastisol encapsulant. Again, the plastisol encapsulated glass fiber mat provides very little improvement to the vinyl floor covering since load is minimally shared by glass fiber reinforcement due to plastisol encapsulation.
U.S. Pat. No. 5,082,708 to Kauffman et al. (hereinafter the '708 patent) discloses a tension floor covering with a reinforcing layer. The vinyl tension floor covering includes a reinforcing layer, preferably disposed below the neutral bending plane. The floor covering elongates in at least one direction due to a controlled pre-stressed condition and tends to return to its original pre-elongated dimensions. Reinforcing layers expand in the across machine direction as well as machine direction in response to tensile stretching forces in the machine direction or roll-up growth. As in U.S. Pat. No. 5,080,944 (discussed and referenced herein above as the '944 patent) the resilient, tension floor covering disclosed by the '708 patent has a continuous matrix surrounding and covering a reinforcing layer. The reinforcing layer has been modified by chemical or mechanical means to have a relaxed compressive stiffness and relaxed tensile stiffness. Due to the relaxation, the floor covering has the ability to elongate under tension, wherein the reinforcing layer is elongated in at least one direction. The total of the elongation and shrinkage, due to aging of the floor covering, is greater than 0.2% as measured over a six week period at room temperature. The fiber mat is cut along mutually non-intersecting line patterns so as to form pivot points that enlarge the cut lines, creating expansion of the mat. Since glass fibers do not elongate in length, it can be only accommodated by slippage of the glass fiber within the plastisol encapsulation. There is no possibility for increasing the overall length of the vinyl floor covering unless the reinforcing fiber slips within plastisol encapsulation. The reinforcing layer is located below the neutral axis of the vinyl floor covering. Again, the plastisol encapsulated glass fiber mat provides very little improvement to the vinyl floor covering since load is minimally shared by glass fiber reinforcement due to plastisol encapsulation.
U.S. Pat. No. 5,935,879 and its divisional U.S. Pat. No. 5,972,166 to Helwig et al. (hereinafter the '879 patent) discloses a non-woven fiber mat and method for forming same. The non-woven fiber mat is suitable for reinforcing resilient sheet floor coverings, such as vinyl floor coverings. The non-woven fiber mat is in the form of a sheet of reinforcement fibers which, at least, includes semi-coiled fibers and can also include coiled fiber, with one or more turns, and even some relatively straight or slightly curved fibers. It is desirable for most, if not all, of the reinforcement fibers to be made from glass. However, it may also be desirable for the reinforcement fibers to include glass fibers and synthetic fibers. It may even be possible for the reinforcement fibers to include only non-glass fibers. At least one polymeric binder is used for bonding together the reinforcement fibers so as to make the fiber mat a suitable substrate for reinforcing resilient sheet floor coverings, such as an interlayer for vinyl floor coverings. By using a non-woven fiber mat containing reinforcement fibers that are not completely straight and capable of interlocking with one another, a resilient sheet floor covering made with such a mat can exhibit improved planar compressibility. The '879 patent discloses that the non-woven fiber mat is wet laid. One or more binders may be used to bind the reinforcement fibers together in the form of a sheet so as to at least enable the base mat to be subsequently processed in-line or wound into a roll for subsequent off-line processing into the present non-woven fiber mat. The binders which may be used with the base mat include thermoplastic-type polymeric binders. These binders can be in particle form (e.g., poly(vinyl alcohol) powder), fiber form (e.g., made from a vinyl chloride copolymer or a copolyester), or a combination of both. These binders are at least partially fused to bond to the reinforcement fibers. The curved sections of the fibers interlock with one another and resist planar elongation and yet allow a greater degree of planar compressive movement than that exhibited by straight fiber mats. The '879 patent discloses a non-woven fiber mat and method for forming the same. Relatively long chopped fibers of glass and other synthetic fibers are mixed and wet laid to form curved segments of glass. These glass segments are bonded together with a primary polymeric binder for ease of handling the non-woven mat through vinyl floor covering manufacturing machinery. A secondary binder is used to rigidly bond the fibers and thereby provide substantial resistance to planar elongation, while allowing for a substantial degree of planar compressive movement. When the flooring expands, the backing of the non-woven fibers correspondingly expands to prevent delamination of the reinforcement layer. It only accommodates compression of the vinyl floor covering. This is due to the rigid bonding of the curved segments of glass fibers by the secondary binder.
U.S. Pat. No. 6,017,835 to Potter (hereinafter the '835 patent) discloses glass compositions for producing dual-glass fibers. Compositions for producing irregularly-shaped dual-glass fibers include a first glass composition and a second glass composition. The first and second glass compositions have nonidentical coefficients of thermal expansion, the difference between the coefficients of thermal expansion being greater than about 2.0 ppm/° C. and preferably 5.0 ppm/° C. These irregularly-shaped glass fibers are suitable for insulation and are produced by extrusion from orifices of a spinner in a rotary process. The first glass composition, A, is preferably a high-borate, low-soda lime-aluminosilicate glass composition having a borate content within the range of from about 14% to about 24% by weight. The second glass composition, B, is preferably a high-soda, low-borate lime-aluminosilicate glass composition having a soda content within the range of from about 14% to about 25% by weight. The liquidus of each of the first and second glass compositions is at least 50° F. (28° C.) below that at which the glass viscosity is 1000 poise. Preferably the liquidus temperature is more than about 200° F. (111° C.) below that at which the glass viscosity is 1000 poise. The difference in coefficient of thermal expansion between glass A and glass B in part gives rise to the irregular shape of the fibers; this difference also controls the degree of bend in individual dual-glass fibers. The difference in the coefficient of thermal expansion must be sufficiently large to cause the right degree of bend in each dual-glass fiber to insure that the fibers are attenuated into irregularly-shaped glass fibers yielding the right amount of entanglement. If the difference is too small, the dual-glass fibers have too large a radius of curvature. The '835 patent discloses glass compositions for producing dual glass fibers. The dual glass spinneret is disclosed for producing a dual glass fiber that has two glasses with differing coefficients of thermal expansion encasing each other and thereby naturally producing a bent fiber that produces the correct degree of entanglement for a non-woven mat used in insulation. There is no indication that this non-woven entangled mat is used in a vinyl floor covering.
Notwithstanding the advances in the field of vinyl floor coverings and related articles with glass fiber reinforcements, there remains a need in the art for a vinyl floor covering that has improved bonding characteristics with sub-flooring. Also needed is a vinyl floor covering that accommodates thermal expansions/contractions and withstands usage stresses without bond delamination. Further needed is a vinyl floor covering that is readily produced in a cost efficient manner. Still further, there is needed a vinyl floor covering that is non-glued and has the ability to float where desired, and remains flat, owing to its enhanced dimensional stability.